In the specification, expressions such as full, half and zero heights are used in expressing heights of cams and pressers and states of butts. In relation to a butt, full height indicates a state when the butt is not subjected to a pressing action of a presser, half height indicates a state when the butt is pressed to be generally half sunken by a second stitch presser, and zero height indicates a state when the butt is subjected to the pressing action of the presser of full height. In relation to the cam and the presser, As the cam and the presser are moved closer to a needle bed, the cam surface is expressed as being increasing in height. The cam of full height is engageable with the butt of half height as well as the butt of full height. The cam of half height is only engageable with the butt of full height. The cam of zero height can allow passage of the butt of full height. A front side of a carriage with respect to a traveling direction thereof is expressed as “the leading side” and a rear side of the same is expressed as “the trailing side”. As to a traveling direction of a needle, a direction in which needles are moved forward to the needle bed gap is expressed as “the front side” and the opposite direction is expressed as “the rear side”. Parts of the stitch cam are also expressed in the same manner: a part of the stitch cam closer to the needle bed gap is expressed as “the front side” and a part of the same far away therefrom is expressed as “the rear side”. In addition, the term, a vertical height, used herein is intended to mean a height with respect to a direction orthogonal to a drawing (a plane of paper).
In general, the stitch cam, which is called a second stitch cam, is used to form different-sized stitches in a course formed at a single traverse of the carriage. The stitch cam has a first stitch size determining cam surface engageable with a butt which is held at the level of the full height without being subjected to a pressing action of a presser (which is hereinafter referred to as “butt of full height”) and a second stitch size determining cam surface only engageable with the butt which is pressed and located at the level of the half height by a second stitch presser of half height (which is hereinafter referred to as “butt of half height”). The second stitch size determining cam surface engageable with the butt of half height is formed in front of the first stitch size determining cam surface engageable with the butt of full height. Due to this, the stitch formed with the needle of the butt of full height is pulled in excessively by the extent corresponding to the step difference between the cam surfaces and thus is increased in size, as compared with the stitch formed with the needle of the butt of half height.
Meanwhile, since a force generated when the needle is retracted increases in proportion to a knitting speed, the butt may undesirably be retracted further beyond the stitch size determining cam surface of the stitch cam. In this case, the stitch cannot be formed at a predetermined stitch size, causing a negative effect on the knitting of a knitted fabric. When the butt is retracted variably, the stitch formed with the needle of the butt of full height and the stitch formed with the needle of the butt of half height may be made indistinguishable from each other or may be reversed in size under certain circumstances.
The applicant of this application for patent previously made a proposal for the stitch cam, as described in JP Laid-open (Unexamined) Patent Publication No. Hei 8-60499 (European Patent Specification No. EP 0698679). The publication discloses the stitch cam wherein a stitch size determining cam surface for the butt of half height and a stitch size determining cam surface for the butt of half height are arranged to be shifted in phase on a common lowering cam surface for lowering both of the butt of half height of the needle and the butt of full height of the needle, so that the former is located at the leading side of the common lowering cam surface and the latter is located at the trailing side thereof, and receiving cams for restricting lowering positions of the butts are arranged in the phase common to that of the stitch size determining cam surfaces so as to correspond in position to them. This stitch cam can solve the problems described above, but, since the stitch cam is designed so that the stitch size determining cam surfaces for the butt of half height and the butt of full height and the receiving cams corresponding to those stitch size determining cam surfaces are all arranged on the single cam, the step difference between the stitch size determining cam surfaces is fixed invariably.
On the other hand, a stitch size adjustable cam is also known, though not shown, which is designed to adjustably vary the step difference between the stitch size determining cam surface for the butt of full height and the stitch size determining cam surface for the butt of half height, so as to adjust proportions of sizes of the stitches formed. Flat knitting machines having this function include, for example, computer-assisted flat knitting machines (e.g. SET-092FF, SIK-102KI (product name)) manufactured by Shima Seiki Mfg., Ltd. These flat knitting machines are designed so that a movable cam having the stitch size determining cam surface for the butt of full height is pivotally mounted on the stitch cam which can act on the butt of full height and the butt of half height and a manual adjusting dial is arranged at the outside of the carriage, so that the movable cam can be changed in position to adjust the stitch step difference by turning the adjusting dial. This flat knitting machine can allow the adjustment of the stitch step difference between the stitch size determining cam surfaces, but, since the stitch cam is not provided with any receiving cam to restrict the lowering positions of the butts, the butts can be retracted excessively beyond the stitch size determining cam surfaces. Further, since the adjustment of the stitch step difference between the stitch size determining cam surface of the movable cam and that of the stitch cam is allowed by changing the position of the movable cam, the orientation of the stitch size determining cam surface of the movable cam adjusted to the position makes a small angle with the orientation of the stitch size determining cam surface of the stitch cam. It is desirable for stitch formation to make the orientation of the stitch size determining cam surface invariable, independently of the stitch step difference, but the second stitch cam of the type designed to allow the adjustment of the stitch step difference by changing the rock position as described above cannot avoid this problem.
It is an object of the present invention to provide a knitting machine having a variable stitch mechanism that can prevent the needles of different height butts being retracted excessively beyond the stitch size determining cam surfaces, while allowing variable adjustment of the stitch step difference between the stitch size determining cam surfaces.